Discharge lamp base and starter



June 13,- 1944. THAYER 2,351,305

DISCHARGE LAMP BASE AND STARTER Filed Feb. 14, 1942 Fig.1.

Invencor: Richard N. Thager, by m/ His A++orneg.

Patented June 13, 1944 DISCHARGE LAMP BASE AND STARTER Richard N.Thayer, Cleveland Heights, Ohio, assignor to General Electric Company, acorporation of New York Application February 14, 1942, Serial No.430,894

2 Claims.

This invention relates to the basing of lamps and discharge devices,including fluorescent tubes or lamps of the positive column dischargetype, and also to the startin control of discharge devices of thischaracter. .An important object of the invention is to provide forincorporating a starter in the lamp structure, and for also includingassociated accessories, particularly the usual capacitor or condenserfor assisting starting and minimizing radio interference as well asarcing. The invention is hereinafter explained with reference to a lampbase containing a starter and a condenser.

Various other features and advantages of the invention will becomeapparent from the description of a species and form of embodiment, andfrom the drawing.

In the drawing, Fig, 1 is a diagrammatic view of a fluorescent tube orlamp equipped with a base or terminal structure embodying my invention,

this base structure being partly broken away and in section, andsuitable circuit connections being diagrammatically illustrated.

Fig. 2 is a tilted inside or rear view of the starter-equipped baseshown in Fig. 1 with part of its skirt or shell broken away, and with adiagrammatic showing of certain circuit connections.

Fig. 3 is a fragmentary tilted or perspective view, partly sectional,showing one end of a lamp tube with the parts of an associated base, andillustrating a stage in the basing of the lamp according to myinvention.

The drawing shows an ordinary fluorescent lamp L (of positive columnelectric discharge type) with a tubular envelope in having thespaced-apart, activated thermionic cathodes ll, 12 in its ends, whichmay be specially heated cathodes of usual coiled filament type, and areshown connected through bipost lamp base or terminal structures B, Cacross a power supply circuit P including the usual ballast H, whichalso serves as a starting inductance, and the manual make-and-breakswitch IS. The envelope it] may contain a low-pressure atmosphere ofstarting gas. such as argon at a pressure of 2 to 5 mm. of mercury, andalso a vaporizable and ionizable working substance such as mercury. Asupply of mercury, which may exceed the amount that will vaporize duringoperation of the lamp L, is indicated by a drop ll inside the envelopeIn, and an internal coating of fluorescent material or phosphor ii onthe envelope walls is also indicated. A starting and electrode-heatingcircuit H is shown connected across the circuit P through the contactterminal biposts I9 01 the bases or terminal structures B, C, thefilamentary cathodes I I, I2 which may be connected between thesebiposts, and the starter S which is interposed between one of thebiposts and the filament II. A capacitor or condenser K of suitablecapacity (e. g., 0.006 microfarad) may be connected across the switch S,to minimize radio interference as well as arcing when the switch S opensand breaks the circuit H, and to assist in starting.

The general mode of operation in starting the lamp L with this circuitarrangement is that when the switch I5 is closed to turn on the lamp L,the switch device S permits flow of current through the circuit H andthe cathode filaments ll, l2 in series therein for a sufficient lengthof time to preheat the cathodes to an adequate emissive temperature, andthen suddenly opens the circuit H; and the resulting voltage kickbetween the cathodes ll, I2 sufiices to initiate discharge betweenthem-or, in other Words, starts the lamp.-

As illustrated, the starter-equipped terminal or base structure B of thelamp L comprises as its main structural element (Figs. 2 and 3) atransverse insulative wall, web, or disc 20 through which the hollowbipost contacts I 9, I! are riveted, and which serves as a base for thestarter switch S, mounted at the inner side of the disc next to the lampenvelope in. In the particular lamp L here illustrated, the end wall ofthe tubular envelope I0 does not involve the disc or web 20, but isformed by the usual glass stern and flare 2| sealed into the end of theenvelope 10. Besides the web or disc 20, the base B comprises a deepsheet metal shell or skirt 22 attached to the disc. As shown, the shellor skirt 22 has one end or margin internally shouldered at 23 andcrimped around the edge of the disc 20 at 24, and has its other endsecured around the end of the glass envelope ID by cement 25. Thecentral portion of the disc 20 is augmented in thickness or reinforcedat its inner side, as by means of a double-ply disc 26 riveted to thedisc 20 by means of the biposts l9, 19. The other base structure C maybe similarly constructed, but not so deep. As thus far described, thesebases B, C resemble those already in use, though the base B isconsiderably deeper than usual.

As shown in Fig. 2, the starter switch S is of thermal type, comprisinga thermostatic strip member 30 which extends parallel to the disc 20closely adjacent its inner side and may be heated by a resistance heater3|, here shown as consisting of fine wire coiled around the member 30over an insulative covering or wrapping 32 of suitably refractorymaterial, such as asbestos paper. At

one end, adjacent the heater 3| the thermostat 30 is fixedly anchored bybeing welded to a supporting stud 33 upstanding from the disc 20. Thisstud 33 may consist of one end of a U-bent wire inserted from the other(outer) side of the disc through suitably spaced holes therein, andsecured by bending its end 34 down on the inner side of the disc. Thethermostatic member is connected by a wire lead to a hollow rivet oreyelet 36 that is riveted through the disc 20. As shown in Fig. 2, thefree end portion of the thermostatic strip 3|] is bent back at 31 in anarc of 180 so as to extend toward its anchored end at 33. Upstandingfrom the disc 28 at a suitable position is a fixed switch contact stud38 which coacts with a movable switch contact 39 afforded or carried bythe free end of the member 30. As here shown, the switch cont-acts 38and 39 consist of (silver) wires extending at right angles to oneanother and welded or soldered into one of the hollow biposts l9 and tothe free end of the thermostat 39, respectively-the wire 39 considerablyextending the retroverted end of the bar 3|] toward its anchorage at 33.The retroversion of the bar at 31 largely compensates for the generalrise of temperature inside the base B due to the heater 3| and to theoperation of the lamp L and the heating of the cathode II, and is alsohelpful in other respects, as explained hereinafter. To the other bipostI9 is soldered or connected one end of the heater coil 3|, and the otherend of this coil is welded or connected to a hollow rivet or eyeletriveted through the disc 20.

The matter of ambient temperature compensation by the J-bentthermostatstrip 30 is of particular importance in the case of a starter Sintimately incorporated in the lamp structure. This is because of thewide range of fluctuation of ambient temperature inside the base B, asbetween the condition when the lamp L has not been in operation for anhour or more and the condition when the lamp L has just been switchedoff after operating for some time and becoming thoroughly heated upabove atmospheric temperature by the discharge and the heating of thecathode II close to the thermostat 38. As the ambient temperaturevariations in the base B affect the-whole thermo-responsive length ofthe member 38 alike, the unbending flexure of the retroverted portion at31 with rising ambient temperature throws the shorter J-arm with itsextension 39 forward toward the contact stud 38, thus acting to offsetthe bodliy backward motion of the portion 31 away from the contact 38due to the concomitant bending back of the longer arm of the strip 38,and tending to maintain contact at 39, 38. A similar but reverse actionoccurs with falling ambient temperature inside the base B. On the otherhand, the local heating of the longer arm of the thermostat strip 38adjacent its anchorage at 33 by the surrounding heater 3| substantiallywithout directly heating the retroversion 31, bends this portion of thestrip 30 backward and so shifts the whole free portion of the J-bentstrip 3|] (including its extension 39) away from contact 38, therebybreaking contact at 39, 38. A similar but reverse action occurs when thecircuit H is opened and heater 3| and the portion of member 3|! withinit cool ofi".

The lead Wires 4|, 4| to the cathode coil H are soldered into the hollowrivets or eyelets 36, 40, thus connectingthis coilinto acircuit of thebase B and lamp Lthat may be traced from circuit H and one bipost l9through the switch contacts 38, 39, the thermostat 39, lead 35, rivet36, one lead 4|, coil other lead 4|, rivet 49, heater coil 3|, to theother bipost I9 and circuit P. The condenser K is shown with its leads42, 42 connected to the bipost I9 that carries the fixed switch contact38 and to the wire 33 that supports the thermostatic member 30, and aslocated to one side of the switch S, being thin enough not to projectabove the upper edge of the member 38 and its heater 3 I.

Basing cement commonly used for attaching bases B, C to the ends of thelamp envelope ID as indicated at 25 in Figs. 1 and 2 requires aconsiderable degree of heat to cure or harden it properly afterapplication. This temperature, however, would be liable to affectunfavorably some of the parts of the switch mechanism S, and especiallythe condenser K, which usually comprises sealing and insulatingcompounds that might be fused by the curing heat, with the result ofvirtually destroying the condenser. To overcome this difliculty, I donot fabricate the complete base .3 by union of disc 20 and shell 22 asusual, but instead make them up and keep them on hand as separate parts:the disc 29 with the biposts |9, |9, the switch mechanism S, and thecondenser K mounted and fully connected thereon; and the shell 22 withthe shoulder 23 formed therein, but without the edge crimping 24. Aftercompletion of the lamp L in other respects, I cement the still uncrimpedshell 22 on one end of the envelope ID, as shown at the left of Fig. 3,and then add the disc 28 and attach it to the shell. To do this, I-maysimply place the disc 20 with its attached parts in the end of the shell2| on the shoulder 23, inserting the cathode leads 4|, 4| through thedisc rivets or eyelets 36, 49; crimp over the shell edge 24 as shown atthe right of Fig. 3, as by working'around the shell with anysuitable'means; and solder the lead wires 4|, 4| into the eyelets (thisis done from the outer side of the disc) and cut oil the ends of thesewires.

The operation of the switch S will be readily understood from theforegoing description, but may be briefly outlined. When the switch I5is open and the whole system is deenergized and has cooled off toambient temperature, the switch S is closed, with the contacts 39,38resiliently pressed together by the springy bimet'al 30, and thestarting circuit H and the cathodes I, I2 are connected across thedischarge circuit P, ready to be energized by closure of the switch l5.When this happens, current flows through the circuits P and H, theswitch S, and the cathodes I I, I2 in series, heating the cathodes. Atthe same time, current flows through the heater 3| of the thermostat 39.which is connected in circuit in series with the contacts 38, 39,gradually heating th heater 3| and the thermostat 38. The transmissionof heat to the resilient thermostatic member30 is slowed by thethermoinsulation 32, which also increases the thermal capacity of thethermostat. As the bimetallic member 38 gradually heats up, it bendsbackward, Fig. 2, away from the fixed contact 38, and the contact 39pulls away from the contact 38 and opens the circuit H through one ofthe biposts I9, while leaving the circuit P energized through the otherbipost l9 and the heater 3| to the cathodes I I, I2. The voltage kickconsequent on breaking the circuit starts the discharge between thecathodes. The discharge current now flows through heater 3|, and thethermostat 30 is thus kept flexed to hold the switch S open as long asthe circuit P remains energized. When the circuit P is de-energized asby opening the switch I5, the heater 3| and the thermostats 30 cool offand the switch S closes, ready for a repetition of the starting cycle asdescribed.

Certain features of the switch S which have only been glanced atheretofore ar of considerable importance in its operation. It has beenusual, heretofore, to provide thermal starting switches with condensersof about 0.05 microfarad capacity-about eight times the 0.006 microfaradcapacity of a condenser K such as there is room for in the base Balongside the switch S--in order to delay the opening of the switch on ahot restart of the lamp L (when it is turned oil? and then at onceturned on again), to give time for proper reheating of the cathodes ll,[2. This is needful because the cathodes ll, l2 cool off far morequickly than does the switch S, when the current to the lamp is shutoff. A condenser of 0.05 microfarad produces adequate delay by causing aminute spot-weld between the contacts 38, 39 when it discharges throughthem as they come together on the turning off of the current; but acondenser of only 0.006 microfarad produces such a very minute weld thatthe reopening of the switch S follows almost instantly when the currentis turned on again quick1ybefore the cathodes H, I! have time to reheatproperly. In my switch S, the inadequacy of the very small condenser Kin this respect is compensated for (in part, at least) by thermalinertia due to the thermal insulation 42; the heat developed in thewinding 3i is transmitted but slowly through the asbestos 32 to thebimetal 30, giving time for reheating the cathodes II, I! before theswitch S reopens. Any delay in the separation of the contacts 38, 39when the member 30 heats that is produced by its retroversion at 31 (asalready mentioned) also tends to compensate for the small capacity ofthe condenser K.

For the convenience of those desiring to use my invention, I giveillustrative particulars of a switch S suitable for a 40 wattfluorescent lamp he usual positive column discharge type, op-

g with a discharge current of some 0.42 ampere and with a cathodepreheat current of some 0.42 to 0.65 ampere, and having a tube ill inchinternal diameter. Assuming a base- Ol 1 2 disc 20 of 1% inch diameteras usual, the anchorage stud 33 may be spaced about 12 to 13 mm. oncenters from the contact stud 38 mounted in the bipost I9, and may belocated nearly /4 iii-ch from the other bipost IS, on centers. Thethermostat member or bar 30 may consist of a strip of the bimetalcommercially known as Chace #2400 Bimetal, composed of laminae of invar,an alloy 01' 64 per cent iron and 36 per cent nickel, and of chromeiron, an alloy of 75 per cent iron, 22 per cent nickel, and 3 per centchromium, in equal thicknesses, welded together; it may be 0.004 inchthick, /8 inch wide, and 20 mm. long before bending. Its dimension fromthe anchorage 33 to the bottom of the 180 bend at 31 may be 16 mm., andthe radius of this bend 31 may be 0.95 mm. The contacts 38 and 33 may beof 25 mil coin silver wire. and the overall length of the contact 39 maybe about '7 mm, with about 1 /2 mm. of its length overlapping the end ofthe member 30 at the weld between them. The heater 3! may be constructedto have a cold resistance of 6 ohms, and may be made of 8 2 turns (plusstraight lead ends) of heating resistance wire such as hereinafterindicated, wound '75 turns per inch around an asbestos-paper wrapping 32on a /8 inch mandrel and then removed from the mandrel, flattenedsufficiently, and then slipped on the bar 30. The wire for this heater3i may consist of about 3% to 4 inches of 6 mil heating resistance wiresuch as is known commercially as "Nichrome V," which is an alloy of percent nickel, 12 per cent iron, 11 per cent chromium, and 2 per centmanganese. The condenser K may have a capacity of about 0.006microfarad, and may be about inch long, /2 inch wide, and 1; inch thick,or slightly more.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A base or terminal structure for an electric discharge device havingtherein a discharge electrode, said structure comprising a disc providedwith contact terminals exposed at one side of the disc, switch meanscomprising a contact and a flexible bimetallic strip anchored by one endat the other side of said disc and exposed to the ambient temperaturethere, and having its free end retroverted and extending back toward theanchored end for coacting with said contact, said strip being arrangedto flex toward said contact at its retroversion with rising temperaturethere while flexing away from said contact adjacent its anchorage withrising temperature there, an electric heater for locally heating saidbimetallic strip adlacent its anchorage substantially without directlyheating its retroversion, and means for connecting said switch means,said electrode, and said heater in circuit between said contactterminals.

2. A base or terminal structure for an electric discharge device havingtherein a discharge electrode comprising electric heating means, saidstructure comprising a disc provided with contact terminals exposed atone side of the disc, switch means comprising a flexible J-bentbimetallic thermostat strip anchored at the other side of the disc byits longer arm, a contact on said disc at the side of the shorter striparm remote from the longer arm, said strip being arranged to flexoutward toward said contact at its retroversion with rising temperaturethere while flexing away from said contact adjacent its anchorage withrising temperature there, an electric heater for locally heating thelonger thermostat strip arm adjacent its anchorage substantially withoutdirectly heating the retroversion of the strip, and means for connectingsaid switch means, said electrode heating means, and said thermostatheater in circuit between said contact terminals.

R'ICHARD N. THAYER.

